Method for sealing a well casing and surrounding strata

ABSTRACT

A method for sealing a well casing, including any perforations that are intentionally provided through the well casing or which may have occurred through the deterioration of the casing, includes the steps of disposing a seal injection assembly that is adapted for ejecting a grout therefrom at a depth that is proximate the perforations in the casing and of ejecting a quantity of a poly-urethane grout through the perforations sufficient to seal the space intermediate the exterior of the casing and the surrounding materials and to also seal the perforations in the casing. If perforations occur at different depths in the casing the process is repeated at the different depths. The perforations are created, if need be, by the use of a well casing perforator that is positioned where a vertical fluid flow is occurring outside the casing. The step of determining where the fluid flow is occurring is accomplished prior to the step of using the well casing perforator. The seal injection assembly is then used to eject the grout as described above through the perforations. If the perforations occur due to a defect arising in the casing, the step of using the well casing perforator may be eliminated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention, in general, relates to bore holes and, more particularly, to a method for preventing the vertical migration of a fluid in the strata surrounding a well casing and for sealing the cracks and openings that occur in deteriorating well casings so as to prevent the vertical migration of the fluid in the casing, as well.

[0003] Normally, the water tables that occur are separated by clay layers (sometimes referred to as lenses) or by rock strata that either prevent or minimize the vertical flow of water and which moderate the flow into an aquifer.

[0004] Whenever a bore hole is drilled, for example, to reach the aquifer, the surrounding strata is disturbed. The act of drilling perforates the lenses and strata which, in turn, provides a path for the migration of water or of other fluids through the perforated lenses and strata. Depending upon the pressures that are encountered, the direction of migration may be either in an upward or in a downward direction.

[0005] The fluid that is prone to migration through the bore hole may be either a clean or a contaminated source of water. If the layers of clay lenses and rock strata are preventing an elevated source of contaminated water from migrating downward and entering into an aquifer that is disposed under the contaminated water, the act of drilling a bore hole can create a vertical migration path that can hasten the migration and the possible subsequent contamination of the aquifer. Clearly, this is to be avoided.

[0006] Not only is contaminated water a concern, but so too are other fluids and other substances that can be carried by a fluid. It is well known that all manner of pollutants have found their way into the ground. The repeated use of various pesticides and insecticides, the careless discarding of toxic substances and petroleum based products, and contamination from leaking storage tanks have contaminated various water tables.

[0007] Some of those toxic substances, either carelessly discarded or from leaking storage tanks, includes radioactive substances as well. Any source of pollution, contamination, or toxicity which can be carried by a fluid such as water is prone to pass through the perforated clay lenses and rock strata which surround a bore hole and contaminate the aquifer.

[0008] The bore hole may be for a water well or for an oil or gas well (or for any other purpose including testing) and it may be of any desired depth. Normally, a casing of some sort is placed in the bore hole and the casing is used to provide an interface intermediate the exterior strata and the interior of the casing. The interior of the casing is then used to convey a fluid (or a gas) to the surface, either directly or by the use of additional interior conduits that are vertically disposed within the casing.

[0009] Cement grout is commonly employed around the casing to minimize the vertical flow path however, this material is subject to fracture from vibration, seismic disturbance, or aging. Additives are commonly used to minimize shrinking of the cement grout, but even this does not change the frangible nature of the cement grout.

[0010] Accordingly, there exists today a need for a method for sealing the strata which surrounds a well casing so as to more effectively prevent the vertical migration of fluids from occurring proximate the well casing (i.e., intermediate the exterior of the well casing and the undisturbed materials adjacent to the bore hole).

[0011] Another problem is that the well casings themselves are subject to failure. Galvanic action, corrosive substances in the strata, as well as the effects of aging, vibration, and seismic disturbance can damage the casing as well. Cracks, holes, or other types of perforation in the casing may then develop over time.

[0012] The fluids that are disposed in the vadose zone may then enter the casing through the cracks and perforations and find a rapid and easy path to lower elevations and even to higher elevations, again depending upon the pressures involved. In this instance, the fractured casing itself becomes a conduit which promotes rapid vertical migration and subsequent contamination of the aquifer.

[0013] The only known solution is to fill the perforated casing with a sealant, such as with cement, in an attempt to form a “plug” that prevents further unwanted vertical migration from occurring in the casing. Clearly, the casing itself must be abandoned in such instances.

[0014] If the need for the casing still exists, yet another bore hole must be drilled and by do doing, another opportunity for any of the problems mentioned hereinabove to once again occur is again created.

[0015] Clearly, a method for sealing a well casing that is perforated (i.e., damaged) is desirable and useful.

[0016] 2. Description of Prior Art

[0017] Well casings and bore holes are, in general, known as are the use of cement grouts that are placed around the casings when they are installed. There is no known method of effectively repairing an old or damaged well casing or of sealing the strata that surrounds the well casing that is comparable with the instant invention. While the structural arrangements of the known types of methods, at first appearance, may have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.

OBJECTS AND SUMMARY OF THE INVENTION

[0018] It is an object of the present invention to provide a method for sealing a well casing and surrounding strata that can be used to seal a casing in a bore hole that is leaking.

[0019] It is also an important object of the invention to provide a method for sealing a well casing and surrounding strata that can be used to seal the strata which surrounds a casing in a bore hole so as to prevent the vertical migration of fluids in the surrounding strata.

[0020] Another object of the invention is to provide a method for sealing a well casing and surrounding strata that can be used to seal a casing in a bore hole that is leaking so as to prevent the vertical migration of fluids from occurring in the casing.

[0021] Still another object of the invention is to provide a method for sealing a well casing and surrounding strata that can be used to repair a damaged casing.

[0022] Still yet another object of the invention is to provide a method for sealing a well casing and surrounding strata that can be used to seal the strata which surrounds a casing in a bore hole so as to prevent the vertical migration of fluids from occurring in the surrounding strata at a predetermined depth of the casing.

[0023] Yet another important object of the invention is to provide a method for sealing a well casing and surrounding strata that can be used to seal the strata which surrounds a casing in a bore hole so as to prevent the vertical migration of fluids from occurring in the surrounding strata at a predetermined depth of the casing by perforating the casing at the predetermined depth and then injecting a polyurethane grout through the newly formed perforations.

[0024] Still yet another important object of the invention is to provide a method for sealing a well casing and surrounding strata that includes the step of injecting a urethane grout through at least one perforation in a well casing.

[0025] Still yet one other important object of the invention is to provide a method for sealing a well casing and surrounding strata that includes the step of determining the various depth locations in a casing where vertical migration of a fluid is occurring in the surrounding strata, followed by the step of perforating the casing at the various depths where it has been determined that vertical migration of the fluid is occurring, and followed by the step of injecting a quantity of urethane grout through the perforations that is sufficient to seal both the perforations and the surrounding strata so as to lessen the vertical migration of the fluid.

[0026] Still yet one other important object of the invention is to provide a method for sealing a well casing and surrounding strata that includes the step of determining the various depth locations in a casing where vertical migration of a fluid is occurring in the surrounding strata, followed by the step of perforating the casing at the various depths where it has been determined that vertical migration of the fluid is occurring, and followed by the step of injecting a quantity of urethane grout through the perforations that are created sufficient to seal both the perforations and the surrounding strata sufficient to stop the vertical migration of the fluid.

[0027] Briefly, a method for sealing a well casing and surrounding strata that is utilized in accordance with the principles of the present invention includes injecting a polyurethane sealant mixture (i.e., a urethane grout) through an opening in a casing that is disposed through a side wall of the casing into a surrounding strata. The opening is either deliberately created or it has occurred as a result of a failure in the casing. The urethane grout penetrates into the surrounding strata and effectively seals the strata while also penetrating and sealing the opening. Accordingly, a method for sealing a well casing and the surrounding strata is provided. As desired, the added step of determining an area (or areas) where leakage in the strata that surrounds the casing is accomplished as well as the added subsequent step of deliberately perforating the casing proximate the area or areas of leakage is also accomplished prior to the step of injecting the urethane grout through the perforations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a cross-sectional view of a well casing showing the method for sealing a well casing and surrounding strata.

[0029]FIG. 2 is a cross-sectional view of well casing showing the method for sealing a well casing and surrounding strata disposed in a vadose zone.

[0030]FIG. 3 is a detailed cross-sectional view of the components of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Referring to all of the drawings and in particular to FIG. 1 is shown, a method for sealing a well casing and surrounding strata, identified in general by the reference numeral 10.

[0032] A first layer of material 12 is disposed below a grade level 14 as is a second layer 16, a third layer 18, a fourth layer 20, a fifth layer 22, and a sixth layer 24, all of which are disposed above an aquifer 26.

[0033] A well casing 28 is disposed in a bore hole and extends into the aquifer 26.

[0034] The first through sixth layers 12, 16, 18, 20, 22, 24 may include any combination of permeable, semi-permeable, or impermeable materials with regard to the flow of a fluid. They may include layers of clay, rock, soil, as well as water tables. Any number of layers are possible such as occur naturally.

[0035] If water is disposed above the aquifer 26, the layers 12, 16, 18, 20, 22, and 24 may be referred to as a vadose zone. The water may be clinging to solid matter in an unsaturated zone above the aquifer 26. A water table or a plurality of water tables (also known as perched water) may also be disposed above the aquifer 26.

[0036] The drilling of the bore hole through the layers 12, 16-24 creates an opening which facilitates the downward or vertical flow of fluid into or out of the aquifer 26. Assuming for a moment that the direction of flow is downward, if any one of the layers, for example the third layer 18, contains contaminants or pollutants 30 suspended in a fluid, the contaminants or pollutants 30 are able to flow down the bore hole past the remaining layers 20, 22, 24 and reach the aquifer 26 which, in turn, can become polluted.

[0037] The well casing 28, when new and undamaged, prevents undesired vertical migration of fluid from occurring therein, however it does not seal the gap that is formed in soils and substances outside of the casing 28 that were disturbed (i.e., loosened) during the drilling of the bore hole.

[0038] Some settling of the soils and substances may occur against the outside of the casing 28, but this is often insufficient to prevent the downward migration of fluid around the casing 28.

[0039] Sometimes, a cement grout 32, which is only partially shown in the drawing, is used to help seal the space outside of the casing, but this solution is less than adequate for the reasons mentioned hereinabove.

[0040] If the casing 28 itself is sound and fluid flow around the casing 28 is believed to be occurring, equipment (not shown) is lowered into the casing 28 to detect the depths at which this is occurring. The equipment may include any known or future means for detecting movement of the fluid in the surrounding layers 12, 16-24 such as acoustic or any other means.

[0041] When the bore hole is originally drilled for a new well, core samples may also be extracted at that time to determine the depths of the various layers 12, 16-24 so that sealing of the impermeable or semi-impermeable layers can occur at optimum depths (i.e., proximate the impermeable and semi-impermeable layers).

[0042] In either case, a well casing perforator (not shown) is positioned at the desired depths in the casing 28 and is used to drill or puncture the well casing 28 as desired. An upper set of perforations 34 and a lower set of perforations 36 are shown in the illustration, although as many perforations as desired are provided wherever needed and at whatever depths are required.

[0043] If desired, additional perforations may be formed at predetermined intervals throughout the entire length (i.e., depth) of the casing 28 for total sealing along the entire longitudinal length thereof.

[0044] The well casing perforator employs any of the known devices and techniques which may be used to perforate the casing 28 as desired. Any quantity or size of the perforations (i.e., holes) may be provided by the well casing perforator which is then removed from the casing 28 after it has formed the desired perforations at any given depth, or if preferred, at a variety of depths.

[0045] Normally, a plurality of perforations are produced by the well casing perforator around the inside circumference (i.e., wall) of the casing 28 sufficient for sealing to occur fully all around the circumference of the casing 28.

[0046] A seal injection assembly, identified in general by the reference numeral 38, is then lowered to any one of the perforations 34, 36 first, although it may be preferred to begin the sealing at the lowest set of perforations, in this instance at the lower set of perforations 36 and then to work upward.

[0047] Obviously, the perforations may be provided at the various depths by raising and lowering the well casing perforator during one basic operation. Then, all of the perforations at the various depths may be sealed. The sealing is described in greater detail hereinbelow. If preferred only one set of perforations at any given depth may be formed in the casing 28 and then that set of perforations can be immediately sealed (to minimize the possibility of any vertical flow occurring in the perforated casing 28). Additional sets of perforations at different depths may then be provided and each new set of perforations may be sealed in its turn.

[0048] The seal injection assembly 38 includes an upper packer 40 and a lower packer 42 which provide a seal (i.e., a barrier) against the interior wall of the casing 28.

[0049] The seal injection assembly 38 is lowered to the desired position so that the upper and lower packers 40, 42 straddle (i.e., contain) the perforations. In the illustration, the upper packer 40 and the lower packer 42 straddle the lower set of perforations 36.

[0050] The packers 40, 42 are well known components in the drilling arts. They may require activation to create and deactivation to release the desired seal or they may simply bear upon the interior wall of the casing 28 as the seal injection assembly 38 is either raised or lowered.

[0051] The packers 40, 42 are mechanically attached to an injector pipe 44 and provide a seal there as well. The injector pipe 44 includes a grout injector apparatus 46 disposed therein and a plurality of holes 48 in the injector pipe 44 that are used to eject a poly-urethane grout 50 therefrom.

[0052] The grout injector apparatus 46 shown is a three-component type of a grout injector, as is disclosed in a prior patent application, Ser. No. 09/121,748 by two of the instant inventors (i.e., Howard and William McCabe) which is approved for issuance as a patent and which is also the parent application for two divisional patent applications. The content thereof is incorporated by reference herein.

[0053] The three component grout injector apparatus 46 is preferred because it allows for optimum grout formulation and for changes in the formulation during injection. However, any type of urethane grout injector apparatus that is adapted to eject the urethane grout 50 is anticipated for use as the grout injector apparatus 46.

[0054] A lead package 52 is attached to the upper end of the seal injection assembly 38 and include ports for three conduits, identified in general by the reference numeral 54, of the grout injector apparatus 46 as well as a control line 56 that is attached to both of the packers 40, 42. The control line 56 is used to activate and to deactivate the packers 40, 42. A common means of activation is to apply a pressure to the packers 40, 42 through the control line 56 that seals the assembly against the casing 28 interior. If preferred, the control line 56 could supply an electrical signal that is used to activate the packers 40, 42.

[0055] A predetermined amount of the urethane grout 50 is formed in the injector pipe 44 and is ejected therefrom through the plurality of holes 48 and out through the lower set of perforations 36 and into the material that surrounds the casing 28. The amount and formulation of the grout 50 that is ejected is sufficient to provide a seal around the casing 28.

[0056] While there are various methods of determining the proper amount of the grout 50 to eject, monitoring the rise of pressure is one way to determine the quantity during ejection. A sudden and substantial rise in pressure in any of the conduits 54 is indicative of completion of the grout ejection operation or process because it indicates that the surrounding area outside of the casing 28 has been sealed and is therefore unable to accept any more grout 50. At that time the ejection of grout 50 is stopped, the packers 40, 42 are deactivated, and the seal injection assembly 38 is either raised or lowered to another depth and the process repeated as desired.

[0057] As a result of the polyurethane foam that is extruded through the casing perforations 34, 36, the grout 50 forms an impermeable seal between the casing 28 exterior and the surrounding materials. In addition, the perforations 34, 36 are themselves sealed during the ejection process thereby restoring the casing 28 into serviceable condition.

[0058] The seal injection assembly 38 provides a means for ejecting the grout 50 through any of the perforations 34, 36 into the surrounding materials and layers 12, 16-24.

[0059] The urethane grout 50 is highly resistant to deterioration over time providing it is not exposed to ultraviolet light. Being disposed in a bore hole, there is little chance of that occurring.

[0060] It also remains flexible, is resistant to vibration and to seismic activity and actually penetrates and surrounds the materials around the casing 28 to which it bonds. It also bonds directly to the casing 28. Accordingly, the grout 50 provides a seal around the casing 28 that greatly resists, and in most instances positively prevents, the vertical flow of fluid proximate the casing 28.

[0061] If the casing 28 already includes a defect perforation 58 that is allowing a fluid to enter into the casing 28 and flow down to the aquifer 26 through the casing 28 (which then serves as an unintentional conduit for the fluid), the seal injection assembly 38 is lowered in the casing 28 so as to have the packers 40, 42 surround the defect perforation 58.

[0062] The grout 50 is then ejected from the seal injection assembly 38 in a quantity sufficient to seal the strata (i.e., the materials) which surround the casing 28 proximate the defect perforation 58 and also to seal the defect perforation 58 in the casing 28 itself.

[0063] Accordingly, a method of sealing defect perforations 58 in the casing 28 is provided which allows continued use of the casing 28 and which stops the possibility of further contamination or pollution caused by migration within the casing 28. While sealing the defect perforations 58 the method also serves to seal the strata that surrounds the casing 28 proximate the defect perforation, as was discussed hereinabove.

[0064] The process is the same for sealing the defect perforation 58 except that the need to use the well casing perforator may be eliminated. If a better seal around the casing 28 is desired, it is of course possible to use the well casing perforator to provide a plurality of perforations proximate the defect perforation 58.

[0065] Casings 28 deteriorate over time. Galvanic action can produce the defect perforation 58 (in a steel casing) as can settling or vibration or seismic activity damage a steel, or any other type of the casing 28. A plurality of defect perforations (not shown) may occur at various depths, all of which can be repaired by a repetition of the processes as disclosed hereinabove.

[0066] Accordingly, old or damaged types of the casing 28 can be repaired so as to permit their continued use.

[0067]FIG. 2 shows the seal injection assembly 38 in an elevated position in which the packers 40, 42 surround the upper set of perforations 34. The grout 50 has been ejected into the strata proximate the casing 28 at both the upper and lower sets of perforations 34, 36, thereby sealing the exterior of the casing 28 where necessary to prevent the vertical flow of fluid around the casing 28. An area of perched water 60 is shown in a vadose zone 62 and is prevented from vertical movement along the exterior of the casing 28 by the process disclosed.

[0068]FIG. 3 is a more detailed view of the seal injection assembly 38. A mechanical termination 64 of the seal injection assembly 38 is shown at the bottom end thereof.

[0069] The invention has been shown, described, and illustrated in substantial detail with reference to the presently preferred embodiment. It will be understood by those skilled in this art that other and further changes and modifications may be made without departing from the spirit and scope of the invention which is defined by the claims appended hereto. 

What is claimed is:
 1. A method for sealing a well casing and surrounding strata, comprising the steps of: (a) disposing means for ejecting a grout proximate a perforation in a casing; and (b) ejecting said grout through said perforation.
 2. The method of claim 1 wherein said step of ejecting said grout includes the step of ejecting a poly-urethane grout.
 3. The method of claim 1 wherein said step of disposing means for ejecting a grout proximate a perforation in a casing includes the step of disposing a seal injection assembly proximate said perforation.
 4. The method of claim 3 wherein the step of disposing a seal injection assembly proximate said perforation includes the step of aligning said seal injection assembly proximate said perforation so that a lower packer is disposed below said perforation and that an upper packer is disposed above said perforation.
 5. The method of claim 4 including the step of activating said lower and said upper packer prior to the step of ejecting said grout through said perforation.
 6. The method of claim 5 including the step of deactivating said lower and said upper packer after the step of ejecting said grout through said perforation.
 7. The method of claim 1 including the step of perforating a sidewall of said casing to provide said perforation prior to the step of disposing means for ejecting a grout proximate a perforation in said casing.
 8. The method of claim 7 including the step of perforating a sidewall of said casing so as to provide a plurality of perforations prior to the step of disposing means for ejecting a grout proximate said plurality of perforations in said casing.
 9. The method of claim 1 wherein the step of disposing means for ejecting a grout proximate a perforation in a casing includes the step of disposing means for ejecting a grout proximate a defect perforation in said casing.
 10. The method of claim 1 including the steps of repeating the steps of: (a) disposing means for ejecting a grout proximate a perforation in a casing; and (b) ejecting said grout through said perforation at a plurality of depths in said casing; wherein at least one additional perforation is provided through said casing at each of said plurality of depths.
 11. The method of claim 10 wherein the repeated include the steps of: (a) disposing means for ejecting a grout proximate a second defect perforation in a casing; and (b) ejecting said grout through said second defect perforation at a plurality of depths in said casing.
 12. The method of claim 1 wherein said step of disposing means for ejecting a grout proximate a perforation in a casing includes the step of disposing a chemical grout injector proximate said perforation.
 13. The method of claim 12 wherein the step of disposing a grout injector proximate said perforation includes the step of disposing a three-component chemical grout injector proximate said perforation.
 14. The method of claim 1 including the step of determining the depth in said casing where a vertical flow of fluid is occurring at an exterior location of said casing followed by the step of perforating a sidewall of said casing proximate said depth in said casing where a vertical flow of fluid is occurring prior to the step of disposing means for ejecting a grout proximate a resulting perforation that is provided in said casing. 